It is standard practice in the size-reduction rolling of a steel strand for the formation of billets, wire, or the like to form the two rolls of each roll stand with radially facing grooves forming an opening through which the workpiece passes. A plurality of such two- or three-high roll stands are arranged in a row with the openings horizontally aligned, and, relative to the normal transport direction of the strand through the stands, the openings are of decreasing cross section. Thus the workpiece is squeezed and stretched as it passes through the succession of stands.
German Pat. No. 1,073,990 describes a triplex roll stand wherein the workpiece starts out with round or triangular section and is passed between three rolls which extend at 120.degree. to each other to form an opening shaped as an equilateral triangle. Such an arrangement allows considerable size reduction in theory, but this possibility is hard to realize because the roll diameter is limited due to the difficulties of mounting the rolls. Also it is fairly difficult to synchronously drive the three rollss, whose surfaces must all move in the same direction and at the same peripheral speed in the opening they form.
Another system for imparting triangular section to a workpiece in a roll stand is described in German patent document 1,176,594. Here only two rolls rotatable about parallel vertically spaced axes are employed so that large roll diameters can be used and so that driving the rolls synchronously is relatively simple. One of the rolls is formed with a V-section groove having a pair of frustoconical flanks flaring radially outward. These two flanks form two sides of a triangular opening whose third side is formd by the cylindrical outer surface of the other roll.
Japanese Pat. No. 54,152,652 assigned to Tanaka has a pair of mainly cylindrical rollers, one of which is formed with a circumferential square-section groove and the other of which is formd with a circumferential square-section groove. A large-diameter ring rides in the groove and serves to strip a workpiece rolled in it from the grooved roller.
The main problem with these arrangements is that the workpiece can only have, measured parallel to the roll axes, a maximum width which is at most as large as the maximum width of the groove, measured axially at the outer surface of the grooved roll. As a result only limited size reduction is possible, so that a great many rolling stands are needed to obtain a size reduction which could theoretically be effected in fewer passes. Any attempt to force too large a workpiece through such a roll stand results inevitably in a burr which cannot be tolerated in a high-quality rolled product.